The present invention relates to stoker type firing equipment for use with an incinerator for refuse (hereinafter called city refuse) coming out of households, plants, etc.
Conventionally, with a city refuse incinerator, a step type stoker, in which movable fire grates and fixed fire grates are combined alternately in a step like manner, allowing the movable fire grates to move back and forth against the fixed fire grates so that refuse is sent forward progressively, has been widely employed as firing equipment.
Stokers located at the upper, middle and lower parts of the aforementioned step type stoker are called respectively "dry stoker" for drying refuse, "combustion stoker" for combustion of the dried refuse, and "post-combustion stoker" for complete combustion of carbon left in combusted residuum, to turn it to ash.
First, city refuse is conveyed into an incinerator and passed onto the dry stoker, and its moisture is evaporated. Next, the dried refuse is passed onto the combustion stoker and combusted. Lastly, carbon found in residue is completely combusted on a post-combustion stoker, to turn it to ash, which is taken out of the incinerator.
A step type stoker for use with a conventional city refuse incinerator is so structured that its primary object is a complete and smooth combustion of city refuse, to turn it to ash with as little unburnt matter as possible.
Due to its structure, the free control of burning rate and burning temperature when burning city refuse is practically impossible using a step type stoker for use with a conventional city refuse incinerator. In reality, a precise control of burning rate and burning temperature when burning city refuse has very seldom been practiced.
On the other hand, due to remarkable recent improvement in living standards in Japan, the calories of refuse has almost reached a level of those of western countries. In Japan where the refuse contains a large amount of waste plastic material due to the extensive use of plastics, the calorific value is especially high.
It is found that a burning temperature reaches 1,200.degree. C.-1,300.degree. C. during the combustion, causing a state of excess burning.
Excess burning may cause damage to a fire grate of the stoker, and produce clinkers on the stoker, thus preventing continuous operation of the incinerator.
Furthermore, it may cause serious environmental pollution because NO.sub.x can easily be generated by a high burning temperature.